1. Field of the Invention
The present invention generally relates to a laser beam power detecting device, and in particular to a laser beam power detecting device for a planar type semiconductor laser diode.
2. Description of the Prior Art
In recent years, the technology of semiconductor advances rapidly accompanying with great progress of the electronic components. The semiconductor laser diode is wildly used in various applications.
With reference to FIG. 1, it shows a perspective view of a prior art semiconductor laser diode. The laser diode is provided with a substrate 18, a first carrier guiding layer 17a, a second carrier guiding layer 17b, and a laser beam emitting section 16. The laser beam emitting section 16 is interposed between the first carrier guiding layer 17a and the second carrier guiding layer 17b, capable of emitting laser beams toward both front and rear ends. For detecting the laser beam power of the laser diode, a light detecting element, such as a light detecting diode, can be used to detect the intensity of the laser power transmitted from the rear end of the laser diode.
However, it is noted that the conventional laser beam power detecting device can not effectively detect the intensity of the laser power of the laser diode, therefore the effect of automatic power controlling is not good. Besides, the output power of the laser diode will be unstable because of affecting of the environment temperature and the heat dissipated by the laser diode during operation.
For stabilizing the output power, the heat of the laser diode must be dissipated by a base, and a light detecting diode is required to detect the laser beam power.
FIG. 2 is a partially cross-sectional view showing a conventional laser beam power detecting device for detecting the laser beam power of a laser diode being assembled in a metal can 14. A window area 15 made of glass material is mounted on a top of the metal can 14. A laser diode 20 is supported on a base and the laser beam transmitted by the laser diode 20 may be emitted out through the window area 15. A light detecting diode 13 is arranged exactly under the laser diode 20 for detecting the intensity of the output power of the laser diode 20.
The light signal received by the light detecting diode 13 will be converted to electric signal and then detected by a control circuit. According to the intensity of the electric signal, the driving current of the laser diode 20 will be adjusted to a suitable value, thereby achieving automatic power controlling. However, this conventional technique is not suitable to be applied in planar type semiconductor laser diode.
It is thus desirable to have a laser beam power detecting device for planar type semiconductor laser diode for overcoming the problems discussed above.
Accordingly, the primary object of the present invention is to provide a laser beam power detecting device particularly designed to be suitable for planar type semiconductor laser diode.
The other object of the present invention is to provide a laser beam power detecting device having better light power detecting effect for the planar type semiconductor laser diode.
To achieve the above objects, in accordance with the present invention, there is provided a laser beam power detecting device comprising a heat dissipation substrate mounted on a printed circuit board, and a laser diode mounted on the heat dissipation substrate. The laser diode is capable of emitting a first laser beam toward a front end thereof and a second laser beam toward a rear end thereof. A light reflecting plate is mounted on the printed circuit board and at a rear area of the heat dissipation substrate for reflecting the second laser beam emitted from the laser diode. A light detecting diode is arranged between the laser diode and the light reflecting plate for receiving the reflected laser beam reflected by the light reflecting plate, thereby detecting an output power of the first laser beam emitted by the laser beam and then controlling the driving current of the laser diode under control of a control circuit. The light reflecting plate is mounted on the printed circuit board at a vertical manner. Alternatively, the light reflecting plate is mounted on the printed circuit board at an inclined angle.
Preferably, the light reflecting plate further comprises two enclosing side plates formed at two side ends of the light reflecting plate. The light reflecting plate may be in a form of protective light reflecting frame comprising a rear reflecting plate having two side ends, two side protecting plates formed at two side ends of the rear reflecting plate, and a top plate forming a protective frame for protecting the laser diode and the light detecting diode.